This invention relates to a processing communication satellite and more particularly relates to uplink reception and transmission techniques for such satellites.
A multibeam processing satellite system requires a comprehensive and consistent approach to its transmission system, including both its uplink and its downlink. Since the uplink and downlink transmission systems are decoupled by the processing (by demodulation, decoding, and switching) on the satellite, these two parts may be defined separately. The uplink transmission system definition must include all aspects relating to the spatial, polarization, spectral, and temporal attributes and, in particular, methods of multiple access to permit many users to utilize the uplink concurrently. Additionally, various data handling issues, including error control and protocol aspects relating to the way that transmission data are organized, must be defined.
The preferred forms of the invention include both uplink transmitting techniques and uplink reception techniques. Regarding the uplink transmitting techniques, a preferred form of the invention is useful for generating and transmitting data in an available spectrum of frequencies suitable for use by a processing satellite. Data cells are provided at one or more earth terminals based on traffic received from one or more user applications. The terminals also provide a synchronizing burst timing signal. Data bursts are generated by coordinating a predetermined number of data cells with a predetermined error correction code, preferably in one or more encoders. The error correction code includes a first error correction code and a second error correction code. The code rate of the first code is a multiple of the code rate of the second code. Data frames are generated from a group of data frame types by coordinating the data bursts with synchronizing bursts timed in response to the synchronizing burst timing signal, preferably by using encoders. Data frames are modulated by a predetermined form of modulation to enable placement of the modulated data frames into a plurality of channels selected from a group of channels having a plurality of channel rates definable in symbols per second, preferably by one or more modulators. The modulated data frames are transmitted over one or more beams with a predetermined form of polarization, preferably by one or more uplink antennas.
The uplink reception techniques are useful for receiving and processing radio carrier signals in an available spectrum of frequencies for use in a processing communication system. One or more beams of the radio carrier signals are received with one or more forms of polarization and modulation, preferably by a reception antenna. The radio carrier signals are demodulated into a plurality of channels including a plurality of channel types having a plurality of channel rates definable in symbols per second, preferably by one or more demodulators. The demodulators demodulate a sufficient number of different frequencies so as to allow up to a predetermined number of bands of frequencies, allow up to a predetermined number of channels of frequencies within each of the bands and allow up to a predetermined number of first subchannels of frequencies or up to a predetermined number of second subchannels of frequencies within each channel. The demodulators also demodulate the channels into data frames including a plurality of data frame types. The data frames are decoded into data bursts and synchronizing bursts, preferably by a decoder circuit. The error correction code includes a first error correction code and a second error correction code. The code rate of the first code is a multiple of the code rate of the second code. Clock signals are generated for timing the demodulation and decoding, preferably by a clock. A synchronizing burst timing signal representative of at least one characteristic of the clock signals is generated, preferably by a signal generator. The timing signal is suitable for transmission to the ground. The decoded data cells are transmitted for further processing, preferably in the satellite.
According to another form of the invention, radio waves are generated for use by a processing communication satellite. The radio waves are generated in one or more beams having one or more forms of polarization and a predetermined form of modulation, and are generated with a sufficient number of different frequencies so as to allow four bands of frequencies and seven channels of frequencies within each of the bands. The channels-have a plurality of channel rates definable in symbols per second and have a channel spacing ratio of about 5/4. The channels also allow five first subchannels of frequencies or 25 second subchannels of frequencies within each channel. The radio waves also are generated to represent data frames having the same duration and defining multiple frequency TDMA channel slots. The data frames have a plurality of data frame types within the channels and subchannels, and the data frame types differ by the number of data bursts and synchronizing bursts transmitted per frame as a function of the channel rates. The radio waves also are generated to represent data bursts and synchronizing bursts within the data frames. At least some of the frames have a number of data bursts which are a multiple of the number of synchronizing bursts. The radio waves also are generated to represent four data cells within the data bursts.
The foregoing techniques offer significant advantages over prior techniques. For example, the preferred forms of the invention permit extensive frequency reuse and permit low power and low cost earth terminals because the modulators and demodulators are organized to allow low speed channels. The modulators and demodulators also are sufficiently flexible to provide for common medium speed usage, such as video conferencing with low end terminals.
The preferred forms of the invention also permit a graceful growth of uplink capacity by concurrent use of multiple frequency channels and deterministic order of transit of uplinked data. The preferred forms of the invention also accommodate existing formats of the pliesiochronous digital hierarchy (PDH) because of higher speed options, and provide two levels of transmission to accommodate adaptation to rain events and to increase usable uplink capacity. The preferred forms of the invention mesh with ATM (asynchronous transfer mode) standards.
The synchronizing bursts of the preferred embodiments provide for continuing time synchronization of terminals whether in the active or standby condition. The preferred frequency placements and symbol rates facilitate digital channelization, and the preferred frequency placement and spectral shaping permit efficient usage of uplink spectrum. In addition, the preferred form of burst format permits coherent demodulation.
The preferred forms of the invention also include error control methods which provide highly efficient usage of uplink power. The time usage techniques provided for in the preferred embodiments permit bandwidth on demand assignments with a small quantum. The described techniques also are well adapted to highly efficient DAMA methods for low duty cycle usage such as xe2x80x9cweb browsing.xe2x80x9d
In summary, the preferred forms of the invention provide uplink transmission and reception, as well as radio wave generation, that are highly efficient, versatile, and accurate.